Filter element and manufacture method thereof

ABSTRACT

A filter element which is improved in filter performance and suitable for use in various types of filters. In the filter element, a multiplicity of tubes each formed of a filtering material and having a substantially circular shape in cross-section are arranged side by side into a tubular assembly with the axes of the tubes lying parallel to one another; inter-tube openings are closed at one end of the tubular assembly which end serves as the inlet side for a fluid to be filtered, whereas intra-tube openings are closed on the opposite end of the tubular assembly; and the total cross-sectional area of all the inter-tube openings, is set smaller than the total cross-sectional area of all the intra-tube openings, but larger than the minimum cross-sectional area of a path through which the fluid is supplied to the tubular assembly. Specifically, one or more filtering materials including a plurality of tubes each having a substantially circular shape in cross-section and connecting portions to interconnect the adjacent tubes are rolled into a spiral shape to provide the tubular assembly with the axes of the tubes arranged side by side parallel to one another.

BACKGROUND OF THE INVENTION

The present invention relates to a filter element suitable for use invarious types of filters such as a vehicle fuel filter and oil filter,for example, and a manufacture method thereof.

For improvement of filter performance, instead of conventional filterelements formed by bending a sheet-like filtering material into theshape of flower leaves or a chrysanthemum in cross-section, there areproposed filter elements of honeycomb structure having an largereffective filtration area per unit volume.

For example, Japanese patent Publication No. 61-50612 or U.S. Pat. No.2,599,604 discloses a filter element which is fabricated by fusing aflat filtering material and a corrugated filtering material to eachother, and then rolling the assembly into a spiral shape to provide acylindrical laminate with a number of small through holes.

In the filter element thus constructed, as shown in FIG. 36, one endface of the cylindrical laminate is sealed off at inlets of flowpassages 91 defined by valley-like portions 71 of a corrugated filteringmaterial 7 and a flat filtering material 8, whereas the other end facethereof is sealed off at outlets of flow passages 92 defined bymountain-like portions 72 of the corrugated filtering material 7 and theflat filtering material 8, while leaving the outlets of the flowpassages 91 open. A fluid to be filtered is introduced to the inlets ofthe passages 92, and the cleaned filtrate is then taken out from theoutlets of the passages 91 after passing through the filtering materials7, 8 for filtration.

However, the above-mentioned structure of the prior art has adisadvantage. The differential pressure between the flow passages 92 onthe inlet side and the flow passages 91 on the outlet side is soincreased due to such factors as the pressure of the fluid to befiltered or clogging of the filtering materials that the flat material 8is deformed (as indicated by dotted lines in FIG. 37). This narrows andeven blocks the flow passages 91 on the outlet side, resulting indegradation of filter performance.

Another problem is in that when rolling the filtering materials togetherinto a spiral shape, the flow passages may be collapsed because of adifference in circumferential length between the inner-side flatfiltering material 8 and the outer-side corrugated filtering material 7.

SUMMARY OF THE INVENTION

The present invention is to solve the problems as set forth above, andhas for its object to provide a filter element which has good filterperformance and is free from such disadvantages as deformation offiltering materials and blockade of the flow passages caused by anincrease in the fluid pressure or the differential pressure. Anotherobject is to prevent collapse of the filtering materials when rolledinto a spiral shape, and to make full use of the volume occupied forfurther improving the filter performance.

The present invention provides a filter element wherein:

a multiplicity of tubes each formed of a filtering material and having asubstantially circular shape in cross-section are arranged side by sideinto a tubular assembly with the axes of the tubes lying parallel to oneanother;

inter-tube openings are closed at one end of the tubular assembly whichend serves as the inlet side for a fluid to be filtered, whereasintra-tube openings are closed on the opposite end of the tubularassembly; and

the total cross-sectional area of all the inter-tube openings is setsmaller than the total cross-sectional area of all the intra-tubeopenings, but larger than the minimum cross-sectional area of a paththrough which the fluid is supplied to the tubular assembly.

In FIGS. 1 and 2, the filter element comprises two sheets of corrugatedfiltering materials 1, 2 which are joined to each other at respectivevalley or bottom portions 12 and 22. The joined filtering materials arerolled into a spiral shape to provided a tubular assembly which has amultiplicity of fluid passages 3 having a substantially circular shapein cross-section and arranged side by side with their axes lyingparallel to each other. The tubular assembly has one end face whereinter-openings, i.e., those openings left between the fluid passages 3are sealed at 52, and another end face where the fluid passages 3intra-openings are closed.

As to the corrugated filtering materials, 1, 2, mountain or top portions11 of the filtering material 1 lying on the inner side, is set to have acircumferential length smaller than mountain or top portions 21 of thefiltering material 2 lying on the outer side.

By changing the spacing between the fluid passage dependent on the innerend and outer sides of the spiral shape such that the adjacent fluidpassages 3 are arranged to be in contact with each other, the effectivefiltration area can be increased.

Preferably, the total cross-sectional area of all the inter-tubeopenings is set smaller than the total cross-sectional area of all theintra-tube openings, but larger than the minimum cross-sectional area ofan inlet path through which the fluid flows.

Further, as shown in FIG. 10, the two sheets of filtering materials 1, 2may be partially joined to each other via bonding regions 51 whileleaving non-bonded regions 19 between the respective bottom portions 12and 22.

In addition, the tubular assembly may be formed by bending one sheet offiltering material to provide a plurality of superposed portions andconnecting portions to interconnect the adjacent superposed portions,and then spreading out the superposed portions into a tubular shape.

The fluid pressure is radially exerted on the tube wall as indicated byarrows in FIG. 11. The present invention has been made with such acharacteristic in mind. Thus, because of the fluid passage 3 having asubstantially circular shape in cross-section, even if the pressure ofthe fluid to be filtered or the differential pressure between interiorand exterior of the fluid passage 3 is increased, the resulting forceswill be evenly applied to the wall of the fluid passage 3 and hence thefluid passage 3 will not deform.

Moreover, by setting the total cross-sectional area of all theinter-tube openings larger than the minimum cross-sectional are of theinlet fluid path, the fluid is not disturbed in its flow and the surfacearea of the fluid passages is kept large for improving the filteringefficiency.

Since the peripheral length of the inner side of the mountain portion 11is shorter than that of the outer side thereof, the filtering materialcan be spirally wound appropriately because of the presence of theperipheral length difference having been previously provided between theouter and inner sides so that no collapse of the fluid passages occurs.

As an alternative, the tubular assembly can be formed easily using onesheet of filtering material, and this permits simplifying themanufacturing.

With the present invention, the fluid passages each having asubstantially circular shape in cross-section makes it possible to avoidany deformation of the filtering materials otherwise caused by anincrease in the fluid pressure or the differential pressure, therebyproviding the filter element with good performance.

With the arrangement that the mountain portions of the filteringmaterial lying on the inner side, are set to have a shortercircumferential length, the fluid passages can be prevented fromcollapsing, and this facilitates the rolling work of the filteringmaterials into a spiral shape.

With the fluid passages lying closely contiguous to each other, a largernumber of fluid passages can be accommodated per unit volume and hencethe filtering efficiency is improved.

Further, with the arrangement that the adjacent fluid passages arearranged to be in contact with each other, or that the two sheets offiltering materials, which constitute the filter element together, arepartially joined to each other, the effective filtration area per unitvolume can be increased to further enhance filter performance.

It is also possible to easily fabricate the tubular assembly using onesheet of filtering material, while simplifying the manufacture steps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 5 illustrate one embodiment of the present invention inwhich;

FIG. 1 is an overall perspective view of a filter element of the presentinvention;

FIG. 2 is a fragmentary sectional view of the filter element;

FIG. 3 and 4 are views showing manufacture steps; and

FIG. 5 is a view showing operation of the filter element of the presentinvention;

FIGS. 6 and 7 are fragmentary enlarged views of the filter elementshowing a second embodiment of the present invention;

FIGS. 8A and 8B are schematic views showing the state of fluid passages3 on the inner and outer peripheral sides of a tubular assembly in thesecond embodiment, respectively;

FIG. 9 is a sectional view of the filter element showing a thirdembodiment of the present invention;

FIG. 10 is a perspective view of a filtering material showing a fourthembodiment of the present invention;

FIG. 11 is a view showing operation of a fluid to be filtered;

FIG. 12 is an overall view showing the construction of a fuel filter inwhich the present invention is incorporated;

FIG. 13 is a characteristic graph showing the relationship of thevolume, number and pressure loss with respect to the outer diameter ofthe fluid passages;

FIGS. 14 and 15 are plan and perspective views of a corrugated filteringmaterial, respectively;

FIG. 16 is a perspective view of an adhesive member;

FIG. 17A and 17B are front views showing the state of two corrugatedfiltering materials before and after bonding therebetween, respectively;

FIG. 18 is a perspective view showing another embodiment of themanufacturing process of the filter element of the present invention;

FIGS. 19 to 21 illustrate a fifth embodiment of the present invention inwhich FIG. 19 is an overall perspective view of the filter element ofthe present invention, and FIGS. 20 and 21 are views showing themanufacturing process of the filter element of FIG. 19;

FIGS. 22 and 23 are fragmentary enlarged views of the filter element ofFIG. 19;

FIGS. 24A and 24B are views showing the manufacture process according toa sixth embodiment of the present invention;

FIGS. 25A and 25B are views showing the manufacturing process accordingto a seventh embodiment of the present invention;

FIGS. 26 and 27 are perspective views showing the filtering materialsaccording to eighth and ninth embodiments of the present invention,respectively,

FIGS. 28A and 28B are schematic views showing the state of fluidpassages on the inner and outer peripheral sides of the tubular assemblyin FIG. 22, respectively;

FIG. 29 is a fragmentary enlarged view of the filter element of FIG. 19;

FIG. 30 is an overall perspective view of the filter element accordingto a tenth embodiment of the present invention;

FIGS. 31 and 32 are views showing the manufacture process according tothe tenth embodiment;

FIGS. 33 and 34 are fragmentary enlarged views of the filter elementshowing modifications of the tenth embodiment;

FIGS. 35A and 35B are views showing the bonding steps to close the fluidpassages; and

FIGS. 36 and 37 are fragmentary enlarged views of a prior art filterelement.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be described with reference toillustrated embodiments.

FIG. 12 shows a fuel tank disposed midway a fuel line for supplying fuelto an engine. A filter element E of the present invention, describedlater in detail, is housed in a filter case F made of iron or resin. Thefilter element E has the upper end fixedly bonded at its outer peripheryto an inner wall of the filter case F by means of an adhesive F1. Thefilter case F is covered with a cover F2 from above, which is fixed atits outer periphery to the upper end opening of the filter case F bycaulking.

Fuel is introduced into the fuel filter from an inlet port F3 disposedat the center of the cover F2 for being filtered through the filterelement E, and then supplied to an engine (not shown) from an outletport F4 disposed at the bottom surface of the filter case F.

FIG. 1 shows the filter element E of the present invention in aperspective view. As shown, the filter element E has a cylindricalshape, and includes a multiplicity of fluid passages 3 each having acircular shape in cross-section and arranged side by side parallel toone another in the axial direction thereof. The filter element E ismanufactured as follows through the process shown in FIG. 3 and 4.

The filter element E comprises, as shown in FIG. 3, two sheets ofcorrugated filtering materials 1, 2, formed by a corrugated roller orthe like to have mountain or top portions 11, 21, each having asubstantially semicircular cross-section, and flat valley or bottomportions 12, 22 lying alternatively, respectively. The corrugatedfiltering material 1, 2 are each made of any desired material such asfilter paper, non-woven cloth, wire netting, or synthetic fabric.Because the flow rate of fuel to be filtered through the fuel filter islower than that of a fluid to be filtered through other oil filters orthe like, the filtering materials 1, 2 with a thickness as thin as 0.14mm can be employed.

The corrugated filtering materials 1, 2 are laid one above the other,and their valley portions 12, 22 are then joined to each other using anadhesive 51 to define tubular spaces (or tubes) surrounded by therespective mountain portions 11, 21, those tubular spaces serving as thefluid passages 3. The filtering materials 1, 2 thus superposed arerolled, as shown in FIG. 4, in a direction transverse to the axes of thefluid passages 3, thereby providing the filter element E in a spiralshape. On this occasion, an adhesive 52 is applied onto the outerperipheries of the fluid passages 3 at one end face of the filterelement E on the side where fuel is introduced, thereby sealing theopenings left between the fluid passages 3. At the other end face, anadhesive 53 is filled in the openings of the fluid passages 3 to closethem. Thus, there are formed the fluid passages 3 open at the fuel inletside and closed at the opposite side, as well as filtrate passages 31,defined between the fluid passages 3, closed at the fuel inlet side andopen at the opposite side (see FIG. 5).

With the above arrangement, the total value ΣS₁ of cross-sectional areasS₁ of the fluid passages 3 shown in FIG. 1 can be made much larger thanthe total value ΣS₂ of cross-sectional areas S₂ of the openingssurrounded by the fluid passages 3 as compared with the prior art,because of the fluid passages 3 each having a tubular shape. Thisincreases the total surface area of the fluid passages 3 and improvesthe filtering capacity to a large extent. Reversely stated, if there isno need of enhancing the filtering capacity, the entire size of thefilter element can be made smaller by reducing the number of fluidpassages 3.

However, the total value ΣS₂ of cross-sectional areas S₂ of the openingssurrounded by the fluid passages 3 must be larger than the minimumcross-sectional area S₃ of the inlet port F3 through which fuel issupplied to the fuel filter, or the outlet port F4, etc. The reason isto avoid the likelihood of disturbing a flow of the fuel (fluid) throughthe flow of passages 3.

The size of outer diameter d of the fluid passage 3 will now beconsidered by referring to FIG. 13. In FIG. 13, the horizontal axisrepresents the outer diameter d (mm), whereas the vertical axisrepresents the element volume V (cm³) and the number of fluid passagesN. Here, solid lines A, B indicate curves for the element volume, brokenlines A₁, B₁ curves for the number of fluid passages, and one-dot chainline C a curve representing pressure loss in the fluid passage.

As will be apparent from FIG. 13, as the outer diameter d of the fluidpassage 3 is set smaller, the total surface area can be increased andhence the element volume V can be reduced as indicated by the solidlines A, B. As indicated by the broken lines A1, B1, however, the numberof fluid passages N must be augmented and this drastically increases thenumber of steps necessary in manufacture. It has also been found thatthe pressure loss in the fluid passage starts increasing when the outerdiameter of the fluid passage is reduced down smaller than 1.5 mm, asindicated by the one-dot chain line C.

Taking into account the above factors of the element volume V, thenumber of fluid passages N and the pressure loss, the highest efficiencyis found in a range of from 1.5 mm to 2.5 mm of the outer diameter d ofthe fluid passage.

Further, as shown in FIG. 2, the filter element E is arranged such thatthe mountain portions 11 of the filtering material 1 lying on the innerside, when rolled into a spiral shape, each have a circumferentiallength smaller than the mountain portions 21 of the filtering material 2lying on the outer side. In other words, the circumferential lengths ofthe mountain portions 11, 21 are set such that the joined portionsbetween the corrugated filtering materials 1, 2 lie on a circle Cdefined by the spiral radius r.

Operation of the filter element E thus fabricated will now be describedwith reference to FIG. 5. Fuel is introduced into the fluid passages 3as indicated by arrows in the figure, and filtered while passing throughthe corrugated filtering materials 1, 2. Between the fluid passages 3,there are defined filtrate passages 31 sealed at the fuel inlet side sothat cleaned fuel is supplied to an engine through the filtrate passages31.

At this time, since the fluid passages are each formed to have asubstantially circular shape in cross-section, it is possible to avoidany deformation of the fluid passages 3 due to the raised pressure ofthe fluid to be filtered or an increase in the differential pressurebetween interior and exterior of the fluid passages 3 caused by cloggingof the filtering materials, thereby preventing degradation of filterperformance. Also, since the mountain portions 11, 21 of the corrugatedfiltering materials 1, 2 are set to have their circumferential lengthscorresponding to the spiral radius r in this embodiment, the fluidpassages will not be deformed or collapsed at their outer peripheralportions when rolled into a spiral shape. This makes full use of thevolume occupied and further improves filter performance.

FIGS. 6 to 8 show a second embodiment of the present invention.

In the above first embodiment, the joined portions of the corrugatedfiltering materials 1, 2, i.e., the valley portions 12, 22 thereof, arearranged to lie on the circle C defined by the spiral radius r, so theadjacent fluid passages 3 on both sides of each joined portions will notcontact each other. However, in the second embodiment, locating thejoined portions on the outer (or inner) side of the circle C defined bythe spiral radius r can bring about a structure in which all adjacentfluid passages 3 are in close contact with each other.

In FIG. 6, the outer-side corrugated filtering material 2 has themountain portions 21 with height lower than the mountain portions 11 ofthe inner-side corrugated filtering material 1. Thus, the mountainportions 11, 21 of the corrugated filtering 1, 2 are set in both theirshapes and circumferential lengths such that the joined portions of thecorrugated filtering materials 1, 2 lie on the outer side of the circleC defined by the spiral radius r, when the corrugated filteringmaterials are folded into a spiral shape with the filtering material 1lying on the inner side (see FIG. 7).

With the above structure, the openings or clearances between each of theadjacent fluid passages 3 are reduced and the density of fluid passages3 per unit volume is augmented to greatly increase the effectivefiltration area. On the contrary, less volume is required to realize thefilter performance equivalent to the prior art, resulting in the reducedsize and weight of the filter element.

Further, when the filtering materials 1, 2 are rolled into a spiralshape, the radius of curvature becomes larger toward the outer peripherysuch that the inner side spiral has the smaller radius of curvature, asseen from FIGS. 8A and 8B. It is, therefore, required for the part ofthe filtering material 2 rolled into the inner side to have a largerlength l1 between the adjacent mountain portions 21 than l₂ for the partthereof rolled into the outer side.

Accordingly, in this embodiment, an arcuate length l₄ of the mountainportion 11 of the filtering material 1 and an arcuate length l₃ of themountain portion 21 of the filtering material 2, as indicated in FIG. 7,are set following the Table 1 below.

                  TABLE 1                                                         ______________________________________                                        l.sub.3 (mm) l.sub.4 (mm)                                                                           Number of Tubes                                         ______________________________________                                        2.0          4.7      249                                                     2.1          4.6      58                                                      2.2          4.5      20                                                      2.4          4.3      14                                                      3.1          3.6       9                                                      ______________________________________                                    

Specifically, by changing the relationship between the arcuate length l3and the arcuate length l4 dependent on the specified number of tubes(tubular spaces) during the rolling step sequentially from the innerside, it is possible to eliminate the clearance between the adjacentfluid passages 3 at maximum, and hence roll the fluid passages into aspiral shape closely.

FIG. 9 shows a third embodiment of the present invention. In thisembodiment, the fluid passages 3 are designed in their array beforehandsuch that the outer periphery of the filter element E becomes asubstantially true circle, and the shapes and circumferential lengths ofthe mountain portions 11, 21 are set corresponding to that design. Whenrolling the filtering materials into a spiral shape, the fluid passages3 are so controlled in their positions that the outer periphery of thefilter element E presents a substantially true circle.

The first embodiment shown in FIG. 1 causes a step difference a at theend position of the rolled filtering materials, and the outer peripheryof the filter element will not come into a perfectly close contact withthe inner peripheral surface of the filter case when the filter elementis housed in the case, thereby making it often difficult to carry outthe sealing work. In this embodiment, however, since the outer peripheryof the filter element has a substantially true circle, the outerperiphery of the filter element is allowed to perfectly closely contactwith the inner periphery surface of the filter case, with the resultthat the sealing work is facilitated. This also enables to effectivelyutilize the space in the case.

FIG. 10 shows a fourth embodiment of the present invention. With thisembodiment, when joining the two sheets of corrugated filteringmaterials, 1, 2 at their valley portions 12, 22, an adhesive 51 is notapplied all over the surface of the valley portions 12, but partiallyapplied to leave non-bonded regions 19. This allows the non-bondedregions 19 to exhibit a filtering function as well, so that theeffective filtration area is increased to improve filter performance.

In the foregoing embodiments, the fluid passages 3 and the openings leftbetween the fluid passages 3 are closed using the adhesives 52, 53 asshown in FIG. 4. Such closing can be performed in other manners as shownin FIGS. 14 to 18.

More specifically, as shown in FIGS. 14 and 15, an adhesive sheet 54made of a polyamide hotmelt adhesive is tentatively bonded to one end ofthe corrugated filtering materials 1, 2 beforehand by hot pressing orso. Here, the adhesive sheet 54 is formed to be 100 μ thick. Thecorrugated filtering material 1 concerned in obtained using a corrugatedroller or the like to shape a belt-like flat filtering material 1 withthe adhesive sheet 54 tentatively bonded to one end thereof, for formingmountain portions 11 each having a substantially semicircular shape incross-section and flat valley portions 12. The resulting corrugatedfiltering material 1 and another corrugated filtering material 2similarly formed are placed one above the other, and then bonded to eachother at their valley portions 12, 22 using the adhesive 51.Subsequently, as shown in FIGS. 17(a) and 17(b), the one ends of thefiltering materials are hot-pressed for mutual adhesion of the adhesivesheets 54 on both the materials, thereby closing the fluid passages 3.

The openings left between the fluid passages 3 can be sealed by puttinga polyamide adhesive member 6, which is formed into a corrugated shapeon both sides as shown in FIG. 16, between the fluid passages 3 at theinlet side while the filtering materials are being rolled, and thenfusing the adhesive member 6 to the opposite ends of the filteringmaterials under heating by hot air or so. More specifically, theadhesive member 6 has a corrugated shape comprising mountain or topportions 61 and valley or bottom portions 62 which correspond to themountain portions 11, 21 and the valley portions 12, 22 of thecorrugated materials 1, 2, respectively. When rolled into a spiralshape, the fluid passages 3 are fitted in the respective valley portions62. The openings left between the fluid passages 3 can thus be sealed byfusing under heating.

Although the bonding method shown in FIG. 4 accompanies a fear of hotallowing the adhesive to be applied to every corner of the tubularspaces and causing partial sealing failure, the method of using theadhesive sheets 54 and bonding them by hot pressing as shown in FIG. 17bmakes it possible to close the fluid passages 3 with high reliabilityand facilitate the manufacture technique.

As to sealing of the openings left between the fluid passages 3,although the foregoing method also has a fear of causing partial sealingfailure at the small gaps between the fluid passages close to eachother, use of the adhesive member 6, having a predetermined width andcorrugated corresponding to the sealed openings left between the fluidpassages when the filtering materials are rolled into a spiral shape,can provide perfect sealability and simplify the bonding steps.

The adhesive sheet 54 and the adhesive member 6 are not limited to thepolyamide adhesive referred above, and may be formed of anotherpolyester or urethane hotmelt adhesive, or epoxy or polyurethaneheat-setting flexible adhesive.

FIGS. 19 to 21 show a fifth embodiment of the present invention. Withthe fifth embodiment, as shown in FIG. 20, one sheet of filteringmaterial 1 is shaped to form superposed portions 13 each comprising apredetermined partial region of the filtering material folded tosuperpose with each other, and flat connecting portions 14 tointerconnect the adjacent superposed portions 13, these two portions 13and 14 lying alternately. A polyamide hotmelt adhesive sheet 55 is thenoverlaid and joined to the filtering material 1 on the flat side. Theadhesive sheet 55 is comprised of an adhesive 55a and a support material55b.

Thereafter, a pin having a circular cross-section is inserted betweenthe filtering material pieces of each superposed portion 13 to form atube 15 having therein a tubular flow passage 3, as shown in FIG. 21.

As with the first embodiment shown in FIG. 4, the filtering materialhaving a multiplicity of tubes 15 or flow passages 3 is rolled in adirection transverse to the axes of the flow passages 3, thereby forminga filter element in a spiral shape.

At this time, the filtering material can be rolled with the tubes 15lying on the inner side, allowing the adjacent tubes 15 to be arrangedin contact with each other, as shown in FIG. 22. Specifically, bysetting the length of the connecting portions 14 to satisfy therelationship of P≈d+α, where d is the diameter of the tube, α is theminimum distance between tubes when laid flat as in FIG. 23 and P is thecenter-to-center pitch of the tubes as indicated in FIG. 23, there canbe obtained the structure in which the flow passages 3 are closelycontiguous with each other when rolled into a spiral shape, enabling toensure the maximum filtration are for the same volume. Note that α isdetermined in the stage of design dependent on the curvature of thespiral shape.

In other words, those tubes 15 rolled on the inner side as shown in FIG.28A is required to have a length l₁ of the connecting portions 14 (orcenter-to-center pitch of the tubes 15) larger than the length l₂ of theconnecting portions 14 between those tubes 15 rolled on the outer sideas shown in FIG. 28B.

Furthermore, in manufacture of the filter element E, since the fluidpassages 3 are formed by folding partial regions of the filteringmaterial to provide the superposed portions 13 and joining the flatadhesive sheet 55 thereto, the manufacture steps can be simplified.

FIGS. 24A, 24B and FIGS. 25A, 25B show a sixth and seventh embodiment,respectively, in which after folding one sheet of filtering material,the open ends of the superposed portions 13 are joined by applying anadhesive 56 to only the recesses or gaps therebetween. This contributesto save the amount of adhesive 56 used.

FIG. 26 shows an eighth embodiment in which the adhesive 57 is appliedto intermittent regions between the connecting portions 14 of thecorrugated filtering material 1 and a flat filtering material 2,parallel to the axes of the superposed portions 13. In a ninthembodiment shown in FIG. 27, the adhesive 57 is applied to intermittentregions extending perpendicular to the axial direction of the superposedportions 13. This embodiment provides non-bonded regions 16 which alsoserve as the filtering surface to increase the effective filtrationarea, while saving the amount of adhesive used.

Although the filtering material is rolled with the tubes 15 and theadhesive sheet 15 lying on the inner and outer sides, respectively, inFIG. 22, it may be rolled with the flow passages 3 and the adhesivesheet 15 lying on the outer and inner sides, respectively, as shown inFIG. 29. In this case, by arranging to satisfy the relationship ofP≈d-α, where d is the diameter of the tube and P is the center-to-centerpitch of the tubes, there can be obtained the structure in which theflow passages are closely contiguous with each other when rolled into aspiral shape.

In that case, however, the superposed portions 13 must be spread out toform the tubes 15 by inserting the pin as shown in FIG. 20,simultaneously with rolling of the filtering material into a spiralshape.

A tenth embodiment shown in FIG. 30 will now be described.

As shown in FIG. 31, filtering materials 1, 2 are shaped to formsuperposed portions 13, 23 and connecting portions 14, 24, respectively,which are then bonded to each other by an adhesive 58. Subsequently, thesuperposed portions 13, 23 are spread out using the tapered pin having acircular cross-section, as shown in FIG. 20, to form tubes 15, 25. Then,as stated above in connection with FIG. 4, fluid passages 32, 33 aresealed at the outlet side to provide the bottom-equipped tubes, and thefiltering materials 1, 2 are rolled into a spiral shape while sealingthe openings left between the fluid passages 32, 33 by an adhesive 52,thereby obtaining a filter element E.

At this time, the diameters d1, d2 of the tubes 15, 25 and thecenter-to-center pitches P1, P2 of the tubes 15, 25 shown in FIG. 32 areset to satisfy the relationships of P2≈d2+α and P1≈d1-α. Here, α isdetermined in the stage of design dependent on the curvature of thespiral shape.

Although the adjacent tubes 15, 25 are apart from each other, whenrolled into a spiral shape, in the tenth embodiment because of thepitches P1, P2 and the tube's diameters d1, d2 set to larger values, itis also possible to arrange the tubes 15, 25 in close contact relationby proper setting of the above parameters, as shown in FIG. 33,resulting in that the maximum filtration area per unit volume can beensured to achieve the maximum efficiency.

Alternatively, as shown in FIG. 34, the pitches of the tubes 15, 25 arenot necessarily equal to each other, and can be set dissimilar asindicated at P4, P5 such that the pitch P4 is larger than pitch P5, forexample.

In addition, the foregoing embodiments may be modified as shown in FIGS.35A and 35B. Specifically, adhesive sheets 59 are bonded to the innerperipheral surfaces of the tubes 15 and/or 25 at one of the endsthereof, and the tubes 15 and/or 25 are hot-pressed to fuse the adhesivesheets 59 for closing the fluid passages 32, 33 defined in the tubes 15,25.

Although the foregoing embodiments have been explained as forming thetubes 15, 25 by inserting the tapered pin having a circularcross-section, they can be formed in such other manners as blastingcompressed air, or pressing the superposed portions 12, 23.

It will be understood that while the plurality of fluid passages 3 areall formed to have the same diameter in the foregoing embodiments, thediameter of the fluid passages 3 can be made different in some partialregions within the scope of the present invention. This modificationenables to partially change the rate of filtration for providing regionswith filter performance different from each other.

Furthermore, the cross-section of the flow passages 3 may be of anelliptical, oval or polygonal shape. Also, the cross-section of thetubular assembly obtained by rolling one or more filtering materialsinto a spiral shape is not limited to a circular shape, and may be of anelliptical, oval or polygonal shape.

What is claimed is:
 1. A filter element comprising;a multiplicity of tubes each formed of a filtering material of substantially uniform thickness and having a substantially circular shape in cross-section and being arranged side by side into a tubular assembly with longitudinal axes of said tubes lying parallel to one another to form inter-tube openings; the inter-tube openings being closed at only one end of said tubular assembly which end serves via intra-tube openings as the inlet side for a fluid to be filtered, intra-tube openings on the opposite end of said tubular assembly being closed; and the total cross-sectional area of all the inter-tube openings being smaller than the total cross-sectional area of all the intra-tube openings, but larger than the minimum cross-sectional area of a path through which the fluid is supplied to said inlet side intra-tube openings.
 2. A filter element according to claim 1, wherein said filter element is used in a fuel filter, and the outer diameter of said tube is set in a range of from 1.5 mm to 2.5 mm.
 3. A filter element comprising;a plurality of tubes each formed of at least one filtering material of substantially uniform thickness and having a substantially circular shape in cross-section, and connecting portions interconnecting said adjacent tubes, said tubes being disposed in a spiral configuration to provide a tubular assembly with the longitudinal axes of said tubes arranged side by side parallel to one another to form inter-tube openings, the inter-tube openings being closed at one end of said tubular assembly which end serves via intra-tube openings as the inlet side for a fluid to be filtered, intra-tube openings on the opposite end of said tubular assembly being closed.
 4. A filter element according to claim 3, wherein the total cross-sectional area of all the inter-tube openings is set smaller than the total cross-sectional area of all the intra-tube openings, but larger than the minimum cross-sectional area of a path through which the fluid is supplied to said filter element.
 5. A filter element according to claim 4, wherein the distance l2 between mountain or top portions of said tubes lying on the outer side is made smaller than the distance l1 between mountain or top portions of said tubes lying on the inner side, when rolled into a spiral shape, for allowing adjacent ones of said tubes to contact with each other.
 6. A filter element according to claim 3, wherein said connecting portions are offset toward the outer periphery side from the radially midpoint between said tubes for making said tubes close to each other.
 7. A filter element according to claim 6, wherein adjacent ones of said tubes are made contact with each other following the relationship of P≈d+α, where d is the outer diameter of said tube, P is the center-to-center pitch of said tubes, and α is the curvature of said rolled spiral shape.
 8. A filter element according to claim 3, wherein said filter element is used in a fuel filter, and the outer diameter of said tube is set in a range of from 1.5 mm to 2.5 mm.
 9. A filter element according to claim 3, wherein said tubes and said connecting portions are integrally made from a piece of said filtering material in such a manner that both ends of adjacent connecting portions are connected to each other by a fixing material so that a remaining portion of said filtering material between said adjacent connecting portions makes said tube.
 10. A filter element for filtering fluid supplied from a supplying path wherein:two sheets of corrugated filtering materials each having a substantially uniform thickness and being formed with mountain portions and valley portions, laid one above the other said sheets being superposed with their mountain portions extending in opposite direction and joined at said respective valley portions to each other; said joined sheets being disposed in configuration to form a tubular assembly which includes a multiplicity of fluid passages each having a substantially circular shape in cross-section and arranged side by side with the axes of said fluid passages lying parallel to one another and filtrate passages formed between said fluid passages; the openings of said filtrate passages being closed at one end face of said tubular assembly, the openings of said fluid passages being closed at the other end face of said tubular assembly; the mountain portions of one of said sheets which lies radically further out in said spiral configuration than the other sheet having a larger circumferential length than the mountain portions of said other sheet; a total cross-sectional area of all of said filtrate passages being smaller than a total cross-sectional area of all of said fluid passages.
 11. A filter element according to claim 10, wherein the ratio of circumferential length of the mountain portions of said filtering material lying on the inner side to circumferential length of the mountain portions of said filtering material lying on the outer side is set to become smaller in the inner peripheral side than in the outer peripheral side of said spiral shape.
 12. A filter element according to claim 11, wherein said filtering materials are each divided into plural zones such that the number of said flow passage is increased gradually toward the outer periphery of said spiral shape, and said ratio is set different for each zone.
 13. A filter element according to claim 10, wherein said two sheets of filtering materials are partially joined to each other for leaving non-bonded regions in said valley portions.
 14. A filter element according to claim 10, wherein adhesive sheets are tentatively bonded to the ends of said two filtering materials at the other end face, and both those ends of said filtering materials are hot-pressed to fuse said adhesive sheets to each other for closing said flow passages.
 15. A filter element for filtering fluid supplied from a supplying path, comprising:a multiplicity of tubes of a filtering material having a substantially uniform thickness, said tubes having a substantially circular cross-sectional shape, said tubes being arranged side by side to be a tubular assembly having an axis substantially parallel to an axis of said tube, so that a plurality of spaces are formed within said tubular assembly between said tubes, one end of said tubes being open to said supplying path and another end of said tubes being closed so that fluid passages to which the fluid from the supplying path is introduced is formed within said tubes, an end of said spaces which corresponds to said one end of said tubes being closed and another end of said spaces being open to form filtrate passages to which the fluid from said fluid passage flows through said filtering material in such a manner that the fluid penetrates through a whole surface of said tubes; a total cross-sectional area of all of said filtrate passages being smaller than a total cross-sectional area of all of said fluid passages.
 16. A filter element according to claim 15, wherein adjacent tubes are connected with each other by a connecting portion.
 17. A filter element comprising:a multiplicity of tubes each formed of a filtering material of substantially uniform thickness and being arranged side by side into a tubular assembly with longitudinal axes of said tubes lying parallel to one another to form inter-tube openings; the inter-tube openings being closed at only one end of said tubular assembly which end serves via intra-tube openings as the inlet side for a fluid to be filtered, intra-tube openings on the opposite end of said tubular assembly being closed; and the total cross-sectional area of all the inter-tube openings being smaller than the total cross-sectional area of all the intra-tube openings, but larger than the minimum cross-sectional area of a path through which the fluid is supplied to said inlet side intra-tube openings.
 18. A filter element comprising:a plurality of tubes each formed of at least one filtering material of substantially uniform thickness, and connecting portions interconnecting said adjacent tubes, said tubes being disposed in a spiral configuration to provide a tubular assembly with the longitudinal axes of said tubes arranged side by side parallel to one another to form inter-tube openings, the inter-tube openings being closed at one end of said tubular assembly which end serves via intra-tube openings as the inlet side for a fluid to be filtered, intra-tube openings on the opposite end of said tubular assembly being closed.
 19. A filter element for filtering fluid supplied from a supplying path wherein:two sheets of corrugated filtering materials each having a substantially uniform thickness and being formed with mountain portions and valley portions, laid one above the other said sheets being superposed with their mountain portions extending in opposite direction and joined at said respective valley portions to each other; said joined sheets being disposed in a spiral configuration to form a tubular assembly which includes a multiplicity of fluid passages each having a substantially circular shape in cross-section and arranged side by side with the axes of said fluid passages lying parallel to one another and filtrate passages formed between said fluid passages; the openings of said filtrate passages being closed at one end face of said tubular assembly, the openings of said fluid passages being closed at the other end face of said tubular assembly; the mountain portions of one of said sheets which lies radically further out in said spiral configuration than the other sheet having a larger circumferential length than the mountain portions of said other sheet; a total cross-sectional area of all of said filtrate passages being smaller than a total cross-sectional area of all of said fluid passages.
 20. A filter element for filtering fluid supplied from a supplying path, comprising:a multiplicity of tubes of a filtering material having a substantially uniform thickness, said tubes being arranged side by side to be a tubular assembly having an axis substantially parallel to an axis of said tube, so that a plurality of spaces are formed within said tubular assembly between said tubes, one end of said tubes being open to said supplying path and another end of said tubes being closed so that fluid passages to which the fluid from the supplying path is introduced is formed within said tubes, an end of said spaces which corresponds to said one end of said tubes being closed and another end of said spaces being open to form filtrate passages to which the fluid from said fluid passage flows through said filtering material in such a manner that the fluid penetrates through a whole surface of said tubes; a total cross-sectional area of all of said filtrate passages being smaller than a total cross-sectional area of all of said fluid passages. 